Recently, relating to the currency of global carbon dioxide emission limits accompanying increased concerns with environment problems, requirement for fuel consumption reduction of automobiles is increasing. In order to satisfy such requirement, with respect to tire performances, reduction of rolling resistance is desired as well. Conventionally, as a method for reducing rolling resistance of tire, optimization of tire structure has been studied. However, currently performed as an ordinary method is to use one with low tan δ (hereinafter referred to as “low loss property”) and excellent low heat generation as a rubber composition applied in a tire.
As a method for obtaining such rubber composition with low heat generation, considered is reduction of fillers such as carbon black, silica and the like, or use of carbon black with large particle size, etc. However, none of the methods is capable of avoiding deterioration of reinforcement performance, wear resistance and gripping performance on wet road surface of the rubber composition.
Then, for example, studied is to blend rubbers with different glass-transition temperatures (Tg), to thereby provide a rubber composition for tire tread appropriate for use in production of a tire excellent in balance of wet gripping performance and low rolling resistance, without deteriorating the wear resistance of the tire (see, e.g. PTL1).